Investigations of phase relations in the system CaONa2OK2OP2O5

The lattice constants of the compound Ca 2 NaK(PO 4 ) 2 have been studied at room temperature using an X-ray powder diffractometer and also in the temperature range from 20 up to 1000 o C by Guinier-Lenne-technology. A hexagonal lattice with the parameters a 0 =5.4367 A and c 0 =7.3125 A and a cell volume of 187.18 A 3 has been determined for the high temperature phase, existing from 670 o C upward. At temperatures below 670 o C a superlattice structure is formed by tripling the axis a, a', and c so that it results in a hexagonal superlattice structure cell with the lattice constants of a 0 =16.311 A and c 0 =21.939 A and cell volume of 5054 A 3